In the prior art, naturally aspirated diesel engines have been converted to operate on a gaseous fuel, for example natural gas, using carburetted technology. However, problems have risen with the use of gas carburettors, particularly when using compressed natural gas (CNG) as a fuel. Furthermore, the advent of turbocharged diesel engines has created further difficulties for most engine converters as the engines are more highly stressed.
The temperature of natural gas after passing through the pressure regulators has been measured to be as low as -40.degree. C. when operating with fully charged CNG cylinders. Gas carburettors deliver fuel on a volume basis rather than a mass (or heat value) basis, and therefore there is a tendency for the carburettors to overfuel the engine. This characteristic affects both naturally aspirated and turbocharged engines with gas carburettors.
Problems also arise due to the design of the intake manifold and carburettor location which can result in some cylinders receiving more or less gas than other cylinders. This causes a tendency for some cylinders to detonate under certain load conditions. Attempts to control this by the use of detonation sensors have not been entirely successful.
A further problem with turbocharged engines is the inability to control the performance of the turbocharger since it is essentially a "free agent" which is not controlled directly by the throttle. Therefore it is also difficult to measure its performance and adjust the fuel flow and boost pressure accordingly.
The Engine Control Unit of the present invention was developed with a view to overcoming one or more of the above-noted problems in the prior art.